U.S. patent number 6,531,257 [Application Number 09/998,354] was granted by the patent office on 2003-03-11 for photosensitive copper paste and method of forming copper pattern using the same.
This patent grant is currently assigned to Murata Manufacturing Co. Ltd. Invention is credited to Masahiro Kubota.
United States Patent |
6,531,257 |
Kubota |
March 11, 2003 |
Photosensitive copper paste and method of forming copper pattern
using the same
Abstract
Provided is a photosensitive copper paste permitting the
formation of a fine and thick copper pattern having high adhesion
to a substrate, and having excellent preservation stability without
causing gelation, and a method of forming a copper pattern, a
circuit board and a ceramic multilayer substrate using the
photosensitive copper paste. The photosensitive copper paste
includes a mixture of an organic binder having an acid functional
group, a copper powder and a photosensitive organic component. The
copper powder has a surface layer having a thickness of at least
0.1 .mu.m from the surface composed CuO as a main component. The
copper powder also has an oxygen content of about 0.8% to 5% by
weight.
Inventors: |
Kubota; Masahiro (Otsu,
JP) |
Assignee: |
Murata Manufacturing Co. Ltd
(N/A)
|
Family
ID: |
18836083 |
Appl.
No.: |
09/998,354 |
Filed: |
November 30, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Nov 30, 2000 [JP] |
|
|
2000-365280 |
|
Current U.S.
Class: |
430/198; 430/15;
430/16; 430/169; 430/192; 430/195; 430/258; 430/260; 430/270.1;
430/280.1; 430/281.1; 430/311; 430/327; 430/330; 430/910 |
Current CPC
Class: |
G03F
7/0047 (20130101); G03F 7/40 (20130101); H05K
3/02 (20130101); C04B 41/009 (20130101); C04B
35/00 (20130101); C04B 41/009 (20130101); C04B
35/10 (20130101); C04B 41/5127 (20130101); C04B
41/0045 (20130101); C04B 41/4539 (20130101); C04B
41/4572 (20130101); C04B 41/5022 (20130101); C04B
41/5188 (20130101); C04B 41/88 (20130101); C04B
41/009 (20130101); C04B 41/5127 (20130101); H05K
1/092 (20130101); H05K 3/4629 (20130101); H05K
2203/0514 (20130101); Y10S 430/111 (20130101); C04B
2111/00844 (20130101); Y10T 428/24917 (20150115) |
Current International
Class: |
G03F
7/40 (20060101); G03F 7/004 (20060101); H05K
1/09 (20060101); H05K 3/02 (20060101); G03C
001/62 (); G03C 001/725 (); G03C 011/12 (); G03F
007/38 (); G03F 007/40 () |
Field of
Search: |
;430/198,258,260,330,311,910,281.1,270.1,280.1,327,169,192,195,15,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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05-287221 |
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Nov 1993 |
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JP |
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06-224538 |
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Aug 1994 |
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JP |
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08-227153 |
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Sep 1996 |
|
JP |
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08-335757 |
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Dec 1996 |
|
JP |
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09-218508 |
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Aug 1997 |
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JP |
|
09-218509 |
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Aug 1997 |
|
JP |
|
09-222723 |
|
Aug 1997 |
|
JP |
|
10-171107 |
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Jun 1998 |
|
JP |
|
Primary Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Dickstein, Shapiro, Morin &
Oshinsky, LLP.
Claims
What is claimed is:
1. A photosensitive copper paste comprising a mixture of an organic
binder having an acid functional group, a copper powder and a
photosensitive organic component; wherein the copper powder has a
surface layer comprising CuO as a main component; and the surface
layer extends from the surface of the powder to a thickness of at
least about 0.1 .mu.m.
2. The photosensitive copper paste according to claim 1, wherein
the copper powder has an average particle diameter of about 1 to 10
.mu.m.
3. The photosensitive copper paste according to claim 2, wherein
the oxygen content of the copper powder is about 0.8% to 5% by
weight.
4. The photosensitive copper paste according to claim 3, wherein
the amounts of the components of the paste are such that the volume
fraction of the residue remaining after burning is about 30% to
89%.
5. The photosensitive copper paste according to claim 4, wherein
the organic binder comprises an acrylic copolymer having a carboxyl
group-containing side chain.
6. The photosensitive copper paste according to claim 5, wherein
the CuO is an in situ layer generated by heating the copper powder
to room temperature or higher in an oxygen-containing
atmosphere.
7. The photosensitive copper paste according to claim 1, wherein
the oxygen content of the copper powder is about 0.8% to 5% by
weight.
8. The photosensitive copper paste according to claim 1, wherein
the CuO is an in situ layer generated by heating the copper powder
to room temperature or higher in an oxygen-containing
atmosphere.
9. The photosensitive copper paste according to claim 1, wherein
the amounts of the components of the paste are such that the volume
fraction of the residue remaining after burning is about 30% to
89%.
10. The photosensitive copper paste according to claim 1, wherein
the organic binder comprises an acrylic copolymer having a carboxyl
group-containing side chain.
11. A method of making the photosensitive paste according to claim
1, comprising: providing a copper powder having a surface layer
comprising CuO as a main component and the surface layer extends to
a thickness of at least about 0.1 .mu.m from the surface of the
powder; and combining said powder with an organic binder having an
acid functional group and a photosensitive organic component.
12. A method of making the photosensitive paste according to claim
11, wherein said providing comprises heating copper powder to at
least room temperature in an oxygen-containing atmosphere.
13. A method of forming a copper pattern comprising applying a
photosensitive copper paste according to claim 1 on a support
member.
14. A method of forming a copper pattern according to claim 13
further comprising: photo-exposing and developing a portion of the
photosensitive copper paste to form a predetermined copper pattern
on the support member; and transferring the copper pattern from the
support member to a substrate.
15. The method of forming a copper pattern according to claim 14,
further comprising preparing the photosensitive copper paste by a
process which comprises heating copper powder to room temperature
or higher in an oxygen-containing atmosphere.
16. The method of forming a copper pattern according to claim 13,
further comprising burning the copper paste.
17. The method of forming a copper pattern according to claim 13,
further comprising: photo-exposing and developing a portion of the
photosensitive copper paste to form a predetermined copper pattern
on the support member; transferring the copper pattern from the
support member to a ceramic green sheet; laminating a plurality of
ceramic green sheets on each of which the copper pattern had been
transferred, to form a laminate, and: burning the laminate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive copper paste used
for forming a desired electrode pattern on a substrate surface or
each of the substrates which constitute a multilayer substrate in
manufacturing a circuit board or a multilayer substrate, or the
like, and a method of forming a copper pattern using the
photosensitive copper paste.
2. Description of the Related Art
Radio-frequency electronic parts used for mobile communication
equipment, satellite receivers, computers, etc. have been
increasingly miniaturized in recent years and concurrently
undergone an increase in performance with miniaturization of these
apparatuses. Also, wiring patterns of the radio-frequency
electronic parts have strongly been required to support an increase
in density and signal transmission speed.
In order to achieve increases in the density and the signal
transmission speed of the wiring patterns of the radio-frequency
electronic parts, the wiring patterns must be made fine while
increasing their thickness (thickening).
A wiring pattern of a radio-frequency electronic part is
conventionally formed by a method comprising forming a pattern on
an insulating substrate by using a conductor paste containing a
conductive metal powder composed of a polyvalent metal such as
copper, and an organic vehicle comprising an organic binder and an
organic solvent, and then drying the pattern and baking the pattern
to form a predetermined wiring pattern.
Although a screen printing method is generally used for forming the
wiring pattern, this method makes it difficult to decrease the
wiring width and the wiring pitch of the wiring pattern to 50 .mu.m
or less in order to obtain a fine wiring pattern. It is generally
recognized that a wiring width and wiring pitch of about 50 .mu.m
or less each are the refining limit of the screen printing
method.
On the other hand, a photolithography method of forming fine and
thick wiring by using a photosensitive conductor paste is proposed
in Japanese Unexamined Patent Application Publication Nos. 5-287221
and 8-227153. This method comprises coating, on an insulating
substrate, a photosensitive conductor paste comprising a conductive
metal powder, an acrylic copolymer having carboxyl groups and
ethylenic unsaturated groups in the side chains thereof, a
photoreactive compound and a photopolymerization initiator, drying
the coating, and then patterning the coating by
photolithography.
Also, a photolithography method of forming fine and thick wiring by
using a photosensitive conductor paste containing a glass powder is
proposed in Japanese Unexamined Patent Application Publication Nos.
6-224538 and 8-335757. In this method, the glass powder is
contained in the photosensitive conductor paste to improve adhesion
between the conductor pattern and the ceramic substrate.
In consideration of the environment, the photolithography method
using a photosensitive conductor paste has recently been desired to
be developed with water or an alkali aqueous solution. Therefore,
an acid functional group having the property of liberating protons,
such as a carboxyl group or the like, is introduced into the
organic binder. However, when a polyvalent metal, particularly
copper, is selected as a conductor for the photosensitive conductor
paste, the copper ions elute and react with the organic binder
anions produced after release of protons to form a
three-dimensional network due to ion crosslinkage, thereby causing
gelation. The gelation of the photosensitive copper paste causes
the problems of difficulties in coating and destabilizing
development even if coating can be performed.
As a method of preventing gelation, for example, Japanese
Unexamined Patent Application Publication No. 9-218509 discloses a
photosensitive conductor paste containing, as a gelation inhibitor,
a phosphorus-containing compound such as phosphoric acid; Japanese
Unexamined Patent Application Publication No. 9-218508 discloses a
photosensitive conductor paste containing a compound having an
azole structure, such as benzotriazole; Japanese Unexamined Patent
Application Publication No. 9-222723 discloses a photosensitive
conductor paste containing an organic compound having a carboxyl
group, such as acetic acid. However, the methods of using the
gelation inhibitor can only slightly lengthen the time to gelation
of the photosensitive copper paste, but difficulties in use of the
photosensitive copper paste remain under the present
conditions.
Also, in Japanese Unexamined Patent Application Publication No.
10-171107, 3-methyl-3-methoxybutanol is used as an organic solvent
for preventing gelation. However, a phenomenon similar to gelation,
i.e., a phenomenon in which a three-dimensional network is formed
by ion crosslinkage to increase the substantial molecular weight,
occurs in the dry paste, thereby causing the problem of failing to
elute an unexposed portion with a developer.
SUMMARY OF THE INVENTION
The present invention has been achieved for solving the above
problems, and an object of the present invention is to provide a
photosensitive copper paste causing less gelation, and exhibiting
excellent storage stability and permitting the formation of a fine
and thick copper pattern having high adhesion to a substrate.
Another object of the present invention is to provide a method of
forming a copper pattern, a circuit board and a ceramic multilayer
substrate using the photosensitive copper paste.
As a result of various experiments and research performed for
achieving the above objects, the inventor found that by using a
copper powder having a surface coating of a copper oxide in a
system containing an organic binder having an acid functional group
and the copper powder, gelation can effectively be inhibited.
Further experiment and examination led to the achievement of the
present invention.
A photosensitive copper paste of the present invention comprises a
mixture of an organic binder having an acid functional group, a
copper powder and a photosensitive organic component, wherein the
copper powder comprises a copper oxide coating on the surface
thereof, and at least the surface layer having a thickness of about
0.1 .mu.m from the surface being composed of CuO as a main
component.
The photosensitive copper paste of the present invention comprises
the copper powder having the surface coating of copper oxide in
which at least the surface layer having a thickness of about 0.1
.mu.m from the surface is composed of CuO as a main component.
Therefore, the occurrence of gelation can be sufficiently
suppressed either in the paste state before coating or in the
coated state after coating and drying. Therefore, the
photosensitive copper paste can be coated, patterned by exposure
and developed, and then baked to efficiently form a fine and thick
copper pattern.
In the photosensitive copper paste of the present invention, the
organic binder having an acid functional group is a wide concept
representing an organic binder comprising a material having a
functional group having the property of releasing protons, such as
a: carboxyl group, a hydroxyl group, a sulfonic group or the like,
or an organic binder containing a material having the functional
group. The type of the acid function group is not limited.
The photosensitive copper paste of the present invention comprises
the copper powder having the surface coating composed of CuO as a
main component at least in the surface layer having a thickness of
about 0.1 .mu.m from the surface thereof. This is because with the
surface layer composed of CuO as a main component and having a
thickness of about 0.1 .mu.m or less, a region (inner layer)
composed of Cu.sub.2 O as a main component readily occurs in the
outermost layer of the copper powder during kneading in the process
for producing the photosensitive copper paste.
In the present invention, "composed of CuO as a main component" is
a concept representing that the molar ratio of CuO exceeds about
50%. The copper powder preferably has an average particle diameter
of about 1 to 10 .mu.m, and the surface layer composed of CuO as a
main component is preferably about 0.1 .mu.m to 1 .mu.m.
The photosensitive organic component used in the photosensitive
copper paste of the present invention is a conventional known
photopolymerizable or photomodifiable compound. Examples of such a
compound include the following: (1) A mixture of a monomer or
oligomer having a reactive functional group such as an unsaturated
group or the like, and a photo-radical generating agent such as an
aromatic carbonyl compound; (2) A diazo resin such as a
condensation product of aromatic bisazide and formaldehyde; and (3)
A mixture of an addition polymerizable compound such as an epoxy
compound, and a photo-acid generator such as a diallyl iodonium
salt or the like; and (4) A naphthoquinone diazide compound.
Of these photosensitive organic components, the mixture of a
monomer or oligomer having a reactive functional group such as an
unsaturated group or the like, and a photo-radical generator such
as an aromatic carbonyl compound is particularly preferred.
Examples of the photo-radical generator include benzyl, benzoin
ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether,
benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate,
4-benzoyl-4'-methyldiphenylsulfide, benzyl dimethyl ketal,
2-n-butoxy-4-dimethyl aminobenzoate, 2-chlorothioxanthone,
2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone,
isopropylthioxanthone, 2-dimethylaminoethyl benzoate, ethyl
p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate,
3,3'-dimethyl-4-methoxybenzophenone, 2,4-dimethylthioxanthone,
1-(4-dodecylphenyl-2-hydroxy-2-methylpropane-1-one,
2,2-dimethoxy-1,2-diphenylethane-1-one, hydroxycyclohexyl phenyl
ketone, 2-hydroxy-2-methyl-1-phenylpropane-1-one,
1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one,
methylbenzoylformate,
1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl) oxime,
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone,
bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,
bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the like.
Examples of the monomer or oligomer having a reactive function
group include hexanediol triacrylate, tripropylene glycol
triacrylate, trimethylolpropane triacrylate, stearyl acrylate,
tetrahydrofurfuryl acrylate, lauryl acrylate, 2-phenoxyethyl
acrylate, isodecyl acrylate, isooctyl acrylate, dodecyl acrylate,
caprolactone acrylate, ethoxynonylphenol acrylate, 1,3-butanediol
diacrylate, 1,4-butanediol diacrylate, diethylene glycol
diacrylate, tetraethylene glycol diacrylate, triethylene glycol
diacrylate, ethoxy bisphenol A diacrylate, propoxyneopentyl glycol
diacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, ethoxy
trimethylolpropane triacrylate, pentaerythritol triacrylate,
propoxy trimethylolpropane, triacrylate, propoxy glyceryl
triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane
tetraacrylate, dipentaerythritol hydroxypentaacrylate, ethoxy
pentaerythritol tetraacrylate, tetrahydrofurfuryl methacrylate,
cyclohexyl methacrylate, isodecyl methacrylate, lauryl
methacrylate, triethylene glycol dimethacrylate, ethylene glycol
dimethacrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol
dimethacrylate, diethylene glycol dimethacrylate, 1,6-hexanediol
dimethacrylate, neopentyl glycol dimethacrylate, 1,3-butylene
glycol dimethacrylate, ethoxy bixphenol A dimethacrylate,
trimethylolpropane trimethacrylate, and the like.
The photosensitive copper paste of the present invention preferably
further contains an ultraviolet absorber. By mixing the ultraviolet
absorber, the absorptivity of exposure light can be improved, and
exposure failure due to light scattering can be minimized. As the
ultraviolet absorber, for example, an azo red pigment, an amine red
dye or the like can be used.
The photosensitive copper paste of the present invention may
further contain an inorganic component such as a glass powder, a
ceramic powder or the like in order to improve adhesion to the
substrate. A known glass powder such as borosilicate glass or the
like can be used as the glass powder, and a known low-temperature
sintering ceramic powder such as alumina, zirconia, crystallized
glass ceramic, glass composite ceramic, non-glass ceramic or the
like can be used as the ceramic powder.
When the inorganic additive such as the glass powder or ceramic
powder contains a polyvalent metal compound, the polyvalent metal
may be at least one selected from the group consisting of boron,
lead, zinc, bismuth, aluminum, magnesium, calcium, barium,
titanium, strontium, zirconium, manganese, cobalt, nickel, iron,
yttrium, niobium, lanthanum and ruthenium.
Examples of the glass powder include powders containing oxides of
polyvalent metals having a valence of two or more, such as a
SiO.sub.2 --PbO system, a SiO.sub.2 --ZnO system, a SiO.sub.2
--Bi.sub.2 O.sub.3 system, a SiO.sub.2 --K.sub.2 O system, a
SiO.sub.2 --Na.sub.2 O system, a SiO.sub.2 --PbO--B.sub.2 O.sub.3
system, a SiO.sub.2 --ZnO--B.sub.2 O.sub.3 system, a SiO.sub.2
--Bi.sub.2 O.sub.3 --B.sub.2 O.sub.3 system, a SiO.sub.2 --K.sub.2
O--B.sub.2 O.sub.3 system, a SiO.sub.2 --Na.sub.2 O--B.sub.2
O.sub.3 system and the like.
Examples of the ceramic powder include powders containing compounds
of polyvalent metals having a valence of two or more, such as
oxides, borides, nitrides and suicides of at least one polyvalent
metal selected from the group consisting of lead, zinc, aluminum,
magnesium, calcium, barium, strontium, zirconium, manganese,
cobalt, nickel, iron, yttrium, lanthanum and ruthenium.
With the inorganic additive containing a polyvalent metal
component, gelation occurs due to reaction with the acid functional
group of the organic binder. In order to prevent reaction between
the polyvalent metal component in the inorganic additive and the
acid functional group of the organic binder, it is effective to add
at least one of the following four additives: (1) Anion-adsorbing
material (2) Thixotropic agent (3) Alcohol having a boiling point
of 178.degree. C. or more (4) Fatty acid amide
The anion-adsorbing material (1) may have the form of inorganic
fine particles or organic fine particles. As the inorganic fine
particles, hydroxyapatite, hydrotalcite, zirconium phosphate,
hydrous antimony oxide and the like are preferably used. As the
organic fine particles, an anion exchange resin or the like can be
used. Examples of the anion exchange resin include the following:
1. A resin comprising a matrix copolymer of divinylbenzene and
acrylate, methacrylate or acrylonitrile, in which a primary,
secondary, tertiary or quaternary amino group is incorporated as an
ion exchange group; 2. A resin comprising a matrix copolymer of
trivinylbenzene and acrylate, methacrylate or acrylonitrile, in
which a primary, secondary, tertiary or quaternary amino group is
incorporated as an ion exchange group; 3. A resin comprising a
matrix copolymer of trimethylolpropane trimethacrylate ester and
acrylate, methacrylate or acrylonitrile, in which a primary,
secondary, tertiary or quaternary amino group is incorporated as an
ion exchange group; and 4. A resin comprising a matrix copolymer of
ethylene glycol dimethacrylate ester and acrylate, methacrylate or
acrylonitrile, in which a primary, secondary, tertiary or
quaternary amino group is incorporated as an ion exchange
group.
As the thixotropic agent (2), an agent generally referred to as a
"thickening, sagging and sedimentation inhibitor" or "sagging and
sedimentation inhibitor", or "pigment wetting, dispersion and
sedimentation inhibitor" can be used.
As the "thickening, sagging and sedimentation inhibitor", a
vegetable polymerized oil system, a polyether-ester surfactant, a
hydrogenated castor oil system, a mixture of a hydrogenated castor
oil system and an amide system, a fatty acid amide wax system or
the like can be used.
As the "sagging and sedimentation inhibitor", a special fatty acid
system, a sulfate ester system, an anionic surfactant, a
polyethylene oxide system, a mixture of a polyethylene oxide system
and amide system or the like can be used.
As the "pigment wetting, dispersion and sedimentation inhibitor", a
fatty acid polyvalent carboxylic acid, a amine salt of
high-molecular weight polyester, a polyether-ester anionic
surfactant, a long-chain amine salt of high-molecular-weight
polycarboxylic acid, a salt of long-chain polyaminoamide and
high-molecular acid polyester, a salt of long-chain polyaminoamide
and phosphoric acid, a special modified polyamide system, a
phosphate ester surfactant, a amidoamine salt of high-molecular
polyester acid or the like can be used.
As the alcohol having a boiling point of 178.degree. C. or more,
either a monohydric or polyhydric alcohol may be used. Examples of
the monohydric alcohol include 1-octyl alcohol, 2-octyl alcohol,
nonyl alcohol, decyl alcohol, 1-methylcyclohexanol,
trimethylcyclohexanol, ethylene glycol monoacetate, diethylene
glycol monobutyl ether, diethylene glycol monoethyl ether,
diethylene glycol monohexyl ether, diethylene glycol monomethyl
ether, diethylene glycol monoethyl ether, diethylene glycol
monovinyl ether, dipropylene glycol monomethyl ether, dipropylene
glycol monoethyl ether, dipropylene glycol monobutyl ether,
ethylene glycol isoamyl ether, ethylene glycol phenyl ether,
ethylene glycol benzyl ether, trimethylhexanol, tetrahydrofurfuryl
alcohol, cresol, butyl lactate, benzyl alcohol, hydroxyethyl
acrylate, phenethyl alcohol, mercaptobutanol, hydroxyethyl
methacrylate, hydroxyethyl piperazine, cyclohexanone oxime,
hydroxymethoxyallyl benzene, hydroxymethoxybenzaldehyde,
hydroxymethylpiperazine, hydroxypropionitrile,
hydroxyactonaphthone, hydroxybenzaldehyde, hydroxyactophenone,
hydroxybenzimidazole, phenylphenol, hydroxybenzoic acid,
hydroxybenzophenone, benzoin, thymol, hydroxymethoxybenzoic acid,
hydroxymethylbenzoic acid, hydroxymethylpyrone, hydroxynaphthoic
acid, hydroxynaphthoquinone, hydroxynorbomene dicarboxyimide,
hydroxyphenyl acetic acid, hydroxyphenyl glycine,
hydroxyphthalimide, hydroxypivalic acid neopentyl glycol ester,
hydroxypropiophenone, hydroxystearic acid, hydroxysuccinic imide,
hydroxytoluic acid, pentaerythritol diacrylate monostearate, and
mixtures thereof.
Examples of the polyhydric alcohol include ethylene glycol,
propylene glycol, trimethylene glycol, butylene glycol,
tetramethylene glycol, pentamethylene glycol, butenediol,
hexamethylene glycol, heptanediol, octanediol, nonanediol,
decanediol, diethylene glycol, dipropylene glycol, triethylene
glycol, tripropylene glycol, glycerin, hexanetriol, heptanetriol,
threitol, erythritol, arabitol, xylitol, ribitol, adonitol,
glucitol, mannitol, iditol, talitol, galactitol, allitol,
perseitol, volemitol and the like.
Examples of the fatty acid amide (4) include acetic amide, lactic
amide, propionic amide, valeric amide, hexanoic amide, heptoic
amide, octanoic amide, decanoic amide, nonanoic amide, stearic
amide, oleic amide, erucic amide and the like.
The photosensitive copper paste of the present invention may
further contain a preservation stabilizer such as a polymerization
inhibitor, an antioxidant, a dye, a pigment, an antifoaming agent,
a surfactant, etc. according to demand.
In the photosensitive copper paste of the present invention, the
oxygen content of the copper powder is preferably about 0.8% by
weight to 5% by weight.
By setting the oxygen content of the copper powder in the range of
about 0.8% to 5% by weight, the occurrence of gelation can be
sufficiently suppressed either in a paste state before coating or
in a coating state after coating and drying.
The reason for setting the oxygen content in the range of about
0.8% by weight to 5% by weight is that with the oxygen content of
the copper powder of less than about 0.8% by weight, the internal
layer composed of Cu.sub.2 O as a main component readily appears in
the outermost layer during kneading, for example, with three rolls
in the process for producing the photosensitive copper paste,
thereby failing to prevent gelation. While with the oxygen content
of the copper powder of over about 5% by weight, the rate of
volumetric shrinkage is increased in the step of reducing and
burning the copper pattern formed by using the photosensitive
copper paste of the present invention, thereby easily causing
disconnection of the formed copper pattern.
In the photosensitive copper paste of the present invention, the
copper powder is coated with a copper oxide by heating the copper
powder to room temperature or higher in an oxygen-containing
atmosphere.
By heating the copper powder to room temperature or higher in the
oxygen-containing atmosphere, the copper powder having the surface
coating of copper oxide can efficiently be obtained, in which at
least the surface layer having a thickness of about 0.1 .mu.m from
the surface is composed of CuO as a main component. Therefore, the
present invention can be made effective.
The reason why the method of heating in the oxygen-containing
atmosphere is preferable as the method of coating the surface the
copper powder with a copper oxide is that this method can easily
control the CuO state of the surface of the copper powder and can
form a dense CuO film.
For example, the present invention can use a copper powder the
surface of which is coated with a Cu oxide by a CuO spray method or
an oxidation method using a solution containing an oxidizing agent.
However, the CuO spray method or the oxidation method using a
solution containing an oxidizing agent cannot easily form a dense
CuO film. Therefore, from the viewpoint of sufficient prevention of
gelation, the copper powder having the surface coated with a Cu
oxide by the method of heating in an oxygen-containing atmosphere
is preferably used.
In the photosensitive copper paste of the present invention, the
volume fraction of the burning residue remaining after burning is
preferably about 30% to 89%. This is because with the volume
fraction of less than about 30%, volumetric shrinkage significantly
occurs during burning to cause disconnection of the formed copper
pattern, while with the volume fraction of over about 89%, the
strength of the formed copper pattern (before burning) is
significantly decreased to cause breakage of the pattern during
burning.
In the present invention, the volume fraction of the burning
residue represents the volume fraction of the inorganic components
(copper, etc.) remaining after burning and contained in a solid
obtained by removing the components (the organic solvent, etc.)
from the photosensitive copper paste during drying.
In the photosensitive copper paste of the present invention, the
organic binder preferably comprises an acrylic copolymer having
carboxyl groups in the side chains. By using the acrylic copolymer
having the carboxyl groups in the side chains as the organic
binder, it is possible to perform development with water or an
alkali aqueous solution while suppressing the occurrence of
gelation. Also, the organic binder is useful as a photosensitive
organic binder.
With the organic binder comprising the acrylic copolymer having the
carboxyl groups in the side chains, the carboxyl groups of the
acrylic copolymer easily react with Cu.sub.2 O in the copper
powder. However, even in such a system, gelation can be securely
suppressed by using the copper powder having the surface coating
composed of CuO as a main component at least in the surface layer
having a thickness of about 0.1 .mu.m from the surface.
Examples of the organic binder comprising the acrylic copolymer
having carboxyl groups in the side chains can be produced by
copolymerizing an unsaturated carboxylic acid and an ethylenic
unsaturated compound. Examples of the unsaturated carboxylic acid
include acrylic acid, methacrylic acid, maleic acid, fumaric acid,
vinylacetic acid, and anhydrides thereof and the like. Examples of
the ethylenic unsaturated compound include acrylic acid esters such
as methyl acrylate, ethyl acrylate and the like; methacrylic acid
esters such as methyl methacrylate, ethyl methacrylate and the
like; fumaric acid esters such as monoethyl fumarate and the like.
As the acrylic copolymer, the following copolymers may be used, in
which an unsaturated bond is incorporated. (1) A copolymer obtained
by adding an acrylic monomer having a functional group such as an
epoxy group or the like, which can react with the carboxyl groups
in the side chains of the acrylic copolymer, to the carboxyl
groups; and (2) A copolymer obtained by reacting the acrylic
copolymer having epoxy groups introduced in place of the carboxyl
groups in the side chains with an unsaturated monocarboxylic acid,
and then introducing a saturated or unsaturated polyhydric
carboxylic anhydride.
A method of forming a copper pattern of the present invention
comprises the steps of applying the photosensitive copper paste of
the present invention on a support member, exposing and developing
the photosensitive copper paste to form a predetermined copper
pattern on the support member, and transferring the copper pattern
formed on: the support member to a substrate.
The method of forming a copper pattern of the present invention
uses the photosensitive copper paste of the present invention,
which comprises the copper powder having the surface coating of
copper oxide in which at least the surface layer having a thickness
of about 0.1 .mu.m from the surface is composed of CuO as a main
component. Therefore, gelation of the photosensitive copper paste
and gelation of the coating after drying can be sufficiently
suppressed to form a fine copper pattern with high precision.
In the present invention, a substrate is a wide concept including
various types of transfer objects, for example, sintered ceramic
substrates such as an alumina substrate and the like, and
unsintered ceramic green sheets, and the like.
A circuit board of the present invention comprises a circuit formed
by forming a predetermined copper pattern by using the
photosensitive copper paste of the present invention, and then
burning the copper pattern.
The circuit board of the present invention comprises a fine and
thick circuit (copper pattern) formed by forming a predetermined
copper pattern by using the photosensitive copper paste of the
present invention, and then burning the copper pattern, thereby
permitting realization of high-density wiring and high-speed signal
which cannot be realized by a conventional circuit board.
A method of producing a ceramic multilayer substrate of the present
invention comprises the steps of applying the photosensitive copper
paste on a support member, exposing and developing the
photosensitive copper paste to form a predetermined copper pattern
on the support member, transferring the copper pattern formed on
the support member to a ceramic green sheet, laminating ceramic
green sheets (on each of which the copper pattern was transferred)
to form a laminate, and burning the laminate.
The method of producing a ceramic multilayer substrate of the
present invention uses the photosensitive copper paste of the
present invention, which comprises the copper powder having the
surface coating of a copper oxide, at least the surface layer
having a thickness of about 0.1 .mu.m from the surface being
composed of CuO as a main component. Therefore, gelation of the
photosensitive copper paste and gelation of the coating after
drying can be sufficiently suppressed to form a fine copper pattern
with high precision, thereby obtaining a ceramic rams multilayer
substrate having excellent adaptability to higher density wiring
and higher speed signals.
The ceramic multilayer substrate of the present invention is
produced by the above described method, and comprises a copper
pattern which is formed by applying the photosensitive copper paste
of the present invention and burning the coating, and which is
provided in the substrate or provided in the substrate and on a
surface thereof.
The ceramic multilayer substrate of the present invention comprises
a fine and thick circuit (copper pattern) formed by forming a
predetermined copper pattern on an insulating substrate by using
the photosensitive copper paste of the present invention, and then
burning the copper pattern, thereby permitting realization of
higher-density wiring and higher-speed signal which cannot be
realized by a conventional ceramic multilayer substrate.
In the present invention, the possible reason why gelation is
suppressed by using the copper powder having the surface coating of
a copper oxide in which at least the surface layer having a
thickness of about 0.1 .mu.m from the surface is composed of CuO as
a main component is the following.
At room temperature in air, the uppermost (outermost) layer of the
copper powder in the level of several nm from the surface is coated
with a copper oxide composed of CuO as a main component, but the
inner region is composed of Cu.sub.2 O as a main component. At room
temperature in air, CuO is more stable than Cu.sub.2 O, and CuO
does not react with the acid functional group in the organic
binder, while the Cu.sub.2 O easily reacts with the acid functional
group in the organic binder. Therefore, in producing the
photosensitive copper paste by using such copper powder, a thin
uppermost layer (the layer composed of CuO as a main component) is
separated during kneading (mixing) of the paste, for example, with
a three roll mill in the process for producing the photosensitive
copper paste, to expose the region (inner layer) composed of
Cu.sub.2 O as a main component to the uppermost layer of the copper
powder, thereby causing gelation due to reaction between Cu.sub.2 O
and the acid functional group in the organic binder.
On the other hand, in the present invention using a copper powder
having the surface coating of a copper oxide in which at least the
surface layer having a thickness of about 0.1 .mu.m from the
surface is composed of CuO as a main component, the region composed
of CuO as a main component has a large thickness, and thus the
region (inner layer) composed of Cu.sub.2 O as a main component
does not appear in the uppermost layer of the copper powder even
during kneading of the paste with the three rolls in the process
for producing the photosensitive copper paste. Therefore, it is
possible to securely suppress the occurrence of gelation due to
reaction between Cu.sub.2 O and the acid functional group in the
organic binder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A, B, C, D and E are sectional views showing a method of
forming a copper pattern according to an embodiment of the present
invention; and
FIG. 2 is a sectional view showing a ceramic multilayer substrate
according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
A method of forming a copper pattern according to an embodiment of
the present invention will be described in detail below with
reference to the drawings.
Although a negative photosensitive copper paste is described as an
example, a positive photosensitive copper paste can also be used by
light-dark inversion of a photomask pattern.
First, as shown in FIG. 1A, a photosensitive paste is coated on a
support member 1 by spin coating, screen printing, a doctor blade,
or the like, and then dried at 40 to 100.degree. C. for 10 minutes
to 2 hours to form a coating film 2 comprising the photosensitive
copper paste.
Next, as shown in FIG. 1B, the coating film 2 on the support member
1 is exposed in a predetermined pattern by irradiation with an
active ray from a high-pressure mercury lamp with an exposure of 20
to 5000 mJ/cm.sup.2 through a mask 5 having a desired pattern
formed therein. As a result, the exposed portions 3a and 3b
irradiated with the ray are cured to form regions which are not
developed by subsequent development.
Next, as shown in FIG. 1C, the coating film 2 comprising the
exposed portions 3 and 3b and the unexposed portions 2a, 2b and 2c
is reacted (i.e., developed) with a. general-purpose alkali aqueous
solution such as a sodium carbonate aqueous solution by a spray
shower method to elute the unexposed portions 2a, 2b and 2c with
the alkali aqueous solution, forming the copper patterns 3a and 3b
on the support member 1.
Next, as shown in FIG. 1D, the copper patterns 3a and 3b on the
support member 1 are heat-transferred to a ceramic green sheet 6 at
1 to 200 MPa and 50 to 150.degree. C. for 5 seconds to 5 minutes by
using a heat press.
Next, as shown in FIG. 1E, the support member 1 is separated from
the ceramic green sheet 6. As a result, the fine and thick copper
patterns (unburned copper patterns) 3a and 3b are formed on the
ceramic green sheet 6.
The method of forming a copper pattern of the present invention is
capable of smoothly coating the photosensitive copper paste on the
support member while suppressing gelation of the photosensitive
copper paste and sufficiently suppressing gelation of a coating
film after drying, thereby permitting stable exposure and
development. Therefore, a fine and thick copper pattern can be
formed on any desired substrate with high precision.
As the transfer support member 1, for example, a film-shaped
support member comprising a polyester film, a polypropylene film, a
nylon film or the like can be preferably used.
In order to improve the transferability of the copper pattern, a
release agent such as a silicon coat, a wax coat, a melamine coat
and the like may be provided on the film-shaped support member.
However, the photosensitive copper paste of the present invention
has excellent transferability, and thus such release agent is not
required. However, in some cases, the property of releasing the
support member from the ceramic green sheet is poor depending upon
the type and amount of the organic binder used for the ceramic
green sheet. In this case, appropriate known surface treatment
(release treatment) can be performed.
As the ceramic green sheet, a sheet formed by molding a slurry
containing a ceramic powder and an organic vehicle can be used.
Also, the ceramic green sheet may further contain a glass powder,
and fine via holes may be formed in a photosensitive ceramic green
sheet containing an organic vehicle and a photosensitive organic
component by photolithography.
More specifically, as the ceramic green sheet, various ceramic
green sheets can be used, which contain, as a ceramic component, an
insulating ceramic powder of Al.sub.2 O.sub.3 or the like, a
dielectric ceramic powder of BaTiO.sub.3 or the like, a ferrite
powder of nickel-zinc ferrite, nickel-zinc-copper ferrite or the
like, a conductive ceramic powder of RuO.sub.2, Pb.sub.2 Ru.sub.2
O.sub.7, Bi.sub.2 Ru.sub.2 O.sub.7, a compound oxide of Mn.Co.Ni or
the like, a piezoelectric ceramic powder such as PZT or the
like.
Although the ceramic green sheet is used as the substrate on which
a copper patter is formed in the first embodiment, the method of
forming a copper pattern of the present invention can be widely
used for various applications such as the formation of a copper
pattern as an electrode on a printed board, etc.
Second Embodiment
FIG. 2 is a sectional view showing a ceramic multilayer substrate
according to an embodiment of the present invention. The ceramic
multilayer substrate is produced by a method of producing a ceramic
multilayer substrate according to an embodiment of the present
invention.
The ceramic multilayer substrate 11 shown in FIG. 2 is a multilayer
circuit board comprising a laminate of insulator layers 12a, 12b,
12c, 12e and 12f, and dielectric layers 13a and 13b.
Also, a capacitor pattern, a coil pattern, a strip line, etc. are
formed in the ceramic multilayer substrate 11 by internal layer
copper patterns 15 and via holes 16.
Furthermore, chip parts 20 such as a chip capacitor and the like, a
thick resistor 21, a semiconductor IC 22, etc. are provided on one
of the main surfaces of the ceramic multilayer substrate 11, and
respectively connected to a surface layer copper pattern 17, the
internal layer copper patterns 15, and the like.
The method of producing the ceramic multilayer substrate 11 will be
described below.
First, a glass powder, a ceramic powder and an organic vehicle are
mixed to prepare slurry for insulator ceramic green sheets.
Similarly, slurry for dielectric ceramic green sheets is prepared.
Next, each of the slurries is formed in a sheet by a doctor blade
method, and then dried at a temperature of 50 to 150 C. to form an
insulator ceramic green sheet and a dielectric ceramic green
sheet.
Then, copper patterns such as a capacitor pattern, a coil pattern
and the like, are formed on each of the ceramic green sheets. Also,
via holes are formed in each of the green sheets according to
demand. The copper patterns are formed according to the method of
forming a copper pattern of the first embodiment.
Next, the ceramic green sheets comprising the copper patterns and
the via holes formed therein are laminated, compression-bonded
together and then burned at a predetermined temperature.
Furthermore, the surface layer copper pattern is formed by the
method of forming a copper pattern of the present invention, and
then burned at a predetermined temperature.
Next, the chip parts 20 and the semiconductor IC 22 are mounted on
the laminate, and the thick resistor 21 is printed thereon to form
the ceramic multilayer substrate 11 shown in FIG. 2.
The method of producing a ceramic multilayer substrate of the
present invention is capable of smoothly coating a photosensitive
copper paste on a support member while suppressing gelation of the
photosensitive copper paste, and sufficiently suppressing gelation
of a coating film after drying, thereby permitting stable exposure
and development. Therefore, a fine and thick copper pattern can be
formed on a ceramic green sheet substrate with high precision.
Then, the ceramic green sheets on which a copper pattern is formed
are laminated, pressure-bonded together and then burned at a
predetermined temperature to sufficiently produce a ceramic
multilayer substrate which can sufficiently support higher-speed
signals and higher-density wiring.
Also, a laminated structure can be formed by coating a mixture
containing a functional organic binder on a substrate or support
member having a fine pattern formed thereon by using the
photosensitive copper paste of the present invention. The laminated
structure is then heat-treated by burning to produce a multilayer
circuit board or a multilayer circuit element. As the mixture
containing a functional organic binder, a mixture comprising the
ceramic powder and an organic binder, a mixture containing a
conductive metal powder of copper, silver or the like, and an
organic binder, and a mixture containing a glass powder can be
used.
Third Embodiment
A method of producing a circuit board (or a circuit element) of the
present invention will be described.
A circuit board of the present invention is produced by coating a
photosensitive copper paste on a substrate by screen printing, spin
coating or the like, drying the coating, performing exposure and
development to form a predetermined copper pattern (unburned copper
pattern), and then heat-treating the copper pattern by burning. The
coating of the photosensitive paste is generally dried at 40 to
100.degree. C. for 10 minutes to 2 hours.
The circuit board produced by the photosensitive copper pattern of
the present invention permits the formation a fine wiring pattern,
for example, having a wiring width and wiring interval of about 50
.mu.m or less each, which cannot be obtained by screen-printing a
conventional photosensitive copper paste. Therefore, it is possible
to sufficiently realize higher-speed signals and higher-density
wiring which cannot be realized by a conventional circuit
board.
In the circuit board of the present invention, various ceramic
green sheets can be used as the substrate, and a glass substrate
can also be used. As the method in which the photosensitive copper
paste of the present invention is coated on a ceramic green sheet
to form a fine and thick copper pattern, and then heat-treated by
burning to produce a circuit board, the method of forming a copper
pattern of the first embodiment (FIG. 1) can be used. However, a
method comprising coating the photosensitive copper paste of the
present invention on a ceramic green sheet and then performing
photolithography to directly form a fine pattern can also be
used.
The circuit board of the present invention may be a substrate for a
circuit element such as a chip capacitor, a chip LC filter or the
like, or a substrate for a module such as VCO (Voltage Controlled
Oscillator), PLL (Phase Locked Loop) or the like.
By using the photosensitive copper paste of the present invention,
development in the photolithography process can stably be carried
out, and thus a fine and thick copper pattern required for an
electronic circuit comprising via holes, wiring, etc. can be
formed, thereby permitting the reliable production of a small
circuit board having excellent radio-frequency properties.
Therefore, it is possible to sufficiently comply with an increase
in the density of radio-frequency chip electronic parts such as a
chip inductor, a chip multilayer capacitor or the like, and an
increase in signal speed.
EXAMPLES
The present invention is described in further detail below with
reference to examples.
Example 1
A copper powder was allowed to stand under conditions of
200.degree. C. and 70 RH% for 24 hours in air to prepare copper
powder A having an oxygen content of 1% by weight and an average
particle diameter of 3 .mu.m.
It was confirmed by observation on a transmission electron
microscope that copper powder A.had a surface layer having a
thickness of 0.1 .mu.m from the surface and composed of CuO as a
main component.
Then, an organic binder, a copper powder, a monomer containing a
reactive functional group, a photopolymerization initiator, an
organic solvent and an ultraviolet absorber were weighed at the
ratio described below, mixed, and kneaded by a three-roll mill to
produce a photosensitive copper paste.
Organic Binder Copolymer (weight average molecular weight=50,000)
at a methacrylic acid/methyl methacrylate copolymerization ratio of
25/75 by weight: 2.0 g
Copper Powder Copper powder A: 15.0 g
Monomer Containing a Reactive Functional Group Trimethylolpropane
triacrylate: 1.0 g
Photopolymerization Initiator
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one: 0.4 g
2,4-diethylthioxanthone: 0.1 g
Organic Solvent Dipropylene glycol monomethyl ether: 5.0 g
Ultraviolet Absorber Azo red pigment: 0.1 g
The photosensitive copper paste formed as described above was
coated on an alumina insulating substrate by a spin coater, and
then dried at 100.degree. C. for 1 hour to form a coating film
having a thickness of 20 .mu.m.
The thus-formed coating film was allowed to stand for 24 hours, and
then exposed to light. In Example 1, the film was irradiated with
light of a high-pressure mercury lamp with an exposure of 50
mJ/cm.sup.2 through a mask having a pattern at a line/space ratio
(L/S) of 20/20 (.mu.m).
Then, development was performed with a sodium carbonate aqueous
solution to obtain a copper pattern having a L/S of 20/20
(.mu.m).
After degreasing, the copper pattern was burned at 900.degree. C.
in an N.sub.2 atmosphere to form a copper pattern having a L/S of
10/30 (.mu.m).
The preservation state (the occurrence of gelation) of the
photosensitive paste having the above composition was observed
immediately after formation, and after 1 day, 3 days, 1 week, 2
weeks, 3 weeks and 1 month of storage at 20.degree. C. in the air.
No gelation occurred in the photosensitive copper paste having the
above composition at any time. It was thus confirmed that the
photosensitive copper paste can be coated on an insulating
substrate by a spin coater and then patterned by photolithography
at any of the times immediately after formation, and 1 day after, 3
days after, 1 week after, 2 weeks after, 3 weeks after and 1 month
after the formation.
Example 2
A CuO powder having a particle diameter of 0.1 .mu.m or less was
sprayed on a copper powder to prepare copper powder B coated with
CuO.
The copper powder B was allowed to stand under the condition of
200.degree. C. in an oxygen-containing atmosphere to prepare copper
powders having various oxygen contents.
Table 1 shows the presence of a CuO-based layer and the oxygen
contents of the copper powder A of example 1, the copper powder B
and untreated copper powder H, and copper powders C, D, E, F and
G.
TABLE 1 Presence of Oxygen Type of copper Method of coating
CuO-based content powder copper oxide layer (% by weight) Copper
powder A Oxidation in air .largecircle. 1 Copper powder B CuO spray
method .largecircle. 1 Copper powder C Oxidation in oxygen-
.largecircle. 0.8 containing atmosphere .largecircle. Copper powder
D Oxidation in oxygen- .largecircle. 0.7 containing atmosphere
.largecircle. Copper powder E Oxidation in oxygen- .largecircle. 5
containing atmosphere .largecircle. 6 Copper powder F Oxidation in
oxygen- .largecircle. 6 containing atmosphere .largecircle. Copper
powder G Oxidation in oxygen- X 1 containing atmosphere Copper
powder H None X 0.2
In Table 1, "Presence of CuO-based layer" represents the results of
observation of each copper powder using a transmission electron
microscope to see whether or not the layer having a thickness of
about 0.1 .mu.m from the surface is composed of CuO as a main
component. In the column of "Presence of CuO-basedlayer",
".largecircle." shows that the layer has a thickness of about 0.1
.mu.m from the surface is composed of CuO as a main component, and
"x" shows that the layer has a thickness of about 0.1 .mu.m from
the surface is composed of Cu.sub.2 O as a main component, not
CuO.
A photosensitive copper paste having the same composition as
Example 1 was prepared by using each of the copper powders A to G.
Then, the preservationstate (the occurrence of gelation) of each of
the photosensitive pastes was observed immediately after formation,
and 1 day, 3 days, 1 week, 2 weeks, 3 weeks and 1 month after the
formation when held at 20.degree. C. in the air. The results are
shown in Table 2 together with the results of the photosensitive
copper paste (Sample No. 1) of Example 1.
TABLE 2 Type of Elapsed time and gelation state Sample copper
Immediately 1 day 3 days 1 week 2 weeks 3 weeks 1 month No. powder
after after after after after after after 1 A .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. 2 B .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. X X 3 C .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. 4 D .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X 5 E
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. 6 F .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. 7 G .largecircle. .largecircle.
.largecircle. .largecircle. X X X 8 H .largecircle. X X X X X X
In Table 2, in evaluation of the gelation state, ".largecircle."
shows that no gelation occurs in the photosensitive copper paste,
permitting coating of the paste, and "x" shows that gelation occurs
in the photosensitive copper paste to make coating of the paste
impossible.
It was confirmed by Table 2 that in the photosensitive copper paste
of Sample No. 8, prepared by using copper powder H which was not
coated with copper oxide, gelation occurred after only one day to
make coating impossible.
It was also found that in the photosensitive copper pastes of
Sample Nos. 1, 3, 5 and 6 prepared by using copper powder coated
with CuO in which the layer having a thickness of about 0.1 .mu.m
from the surface was composed of CuO as a main component, and the
oxygen content of the copper powder was about 0.8% by weight,
gelation was sufficiently prevented to permit coating of the paste
even 1 month after formation.
It was further found that in the photosensitive copper paste
prepared by using copper powder G in which the layer having a
thickness of about 0.1 .mu.m from the surface was not composed of
CuO as a main component, the time to gelation was longer than the
photosensitive copper paste of Sample No. 8 prepared by using
copper powder H not coated with copper oxide, but gelation occurred
in the photosensitive copper paste with the passage of time to make
coating of the paste impossible.
It was further found that in the photosensitive copper paste of
Sample No. 2 prepared by using copper powder B coated with CuO by
the spray method, rather than oxidation in the oxygen-containing
atmosphere, and the photosensitive copper paste of Sample No. 4
prepared by using copper powder D having an oxygen content of less
than about 0.8% by weight, gelation occurred within a relatively
short time, as compared with the photosensitive copper pastes of
Sample Nos. 1, 3, 5 and 6. However, in Samples Nos. 2 and 4, the
time to gelation significantly lengthened as compared with Sample
No. 8 prepared by using copper powder H not coated with copper
oxide, thereby causing an effect to some extent.
Furthermore, exposure, development and burning were carried out by
using the photosensitive copper pastes of Samples Nos. 3, 5 and 6
by the same method as Example 1. With the photosensitive copper
pastes of Sample Nos. 3 and 5, no disconnection occurred in the
copper pattern, while with the photosensitive copper paste of
Sample No. 6 having an oxygen content of over about 5% by weight
(oxygen content of 6% by weight), disconnection was observed in the
formed copper pattern.
These result indicate that with an oxygen content in the range of
about 0.8% to 5% by weight, a most preferable result is
obtained.
Example 3
(1) A slurry obtained by mixing 37.3 g of borosilicate glass
powder, 24.9 g of alumina powder, 6.2 g of copolymer (weight
average molecular weight=50,000) having a methacrylic acid/methyl
methacrylate copolymerization ratio of 25/75 by weight, 3.1 g of
ethanol and 0.5 g of dipropylene glycol monomethyl ether was formed
in a sheet by the doctor blade method, and then dried at
100.degree. C. for 1 hour to obtain a ceramic green sheet having a
thickness of 30 .mu.m.
(2) Next, a copper pattern having a L/S of 20/20 (am) was formed on
a polyethylene terephthalate (PET) film by using the photosensitive
paste of Example 1 by the same method as Example 1.
(3) Next, the PET film was superposed on the ceramic green sheet,
then heat-pressed under the conditions of 10 MPa and 60.degree. C.
for 1 minute and then the PET film was separated to heat-transfer
the copper pattern onto the ceramic green sheet. The same process
was repeated to obtain five ceramic green sheets on each of which a
copper pattern was formed.
(4) Next, the thus-formed ceramic green sheets were laminated and
then heat-pressed under the conditions of 200 MPa and 60.degree. C.
for 1 minute.
(5) Then, the resultant multilayer pressure-bonded product was
burned at 900.degree. C. in N.sub.2.
As a result, a ceramic multilayer substrate (multilayer alumina
substrate) containing copper patterns with a LIS of 10/30 (.mu.m)
was obtained.
Example 4
(1) A slurry (the same slurry as Example 3) obtained by mixing 37.3
g of borosilicate glass powder, 24.9 g of alumina powder, 6.2 g of
copolymer (weight average molecular weight=50,000) having a
methacrylic acid/methyl methacrylate copolymerization ratio of
25/75 by weight, 3.1 g of ethanol and 0.5 g of dipropylene glycol
monomethyl ether was coated, by the doctor blade method, on a PET
film on which a copper pattern was formed by the same method as
Example 3.
(2) After drying at 50.degree. C. for 1 hour and heat-pressing
under the conditions of 10 MPa and 60.degree. C. for 1 minute, the
PET film was separated to form a ceramic green sheet on which the
copper patter was formed. The same process was repeated to form
five ceramic green sheets on each of which a copper pattern was
formed.
(3) Next, the thus-formed ceramic green sheets were laminated, and
then heat-pressed under the conditions of 200 MPa and 60.degree. C.
for 1 minute.
(5) Then, the resultant multilayer pressure-bonded product was
burned at 900.degree. C. in N.sub.2.
As a result, a ceramic multilayer substrate (multilayer alumina
substrate) containing copper patterns with a LUS of 10/30 (.mu.m)
was obtained.
A photosensitive copper paste of the present invention comprises a
copper powder having a surface coating of a copper oxide, the
surface layer having a thickness of about 0.1 .mu.m from the
surface being composed of CuO as a main component. Therefore, the
occurrence of gelation can be sufficiently suppressed either in the
paste state before coating or in the coated state after coating and
drying. Therefore, the photosensitive copper paste can be coated,
patterned by exposure and development, and then baked to
efficiently form a fine and thick copper pattern.
When the oxygen content of the copper powder is about 0.8% by
weight to 5% by weight, the occurrence of gelation can be
sufficiently suppressed either in the paste state before coating
and in the coated state after coating and drying, thereby making
the present invention more effective.
When the copper powder is coated with a copper oxide by heating the
copper powder to room temperature or higher in an oxygen-containing
atmosphere, the copper powder having the surface coating of a
copper oxide in which at least the surface layer having a thickness
of about 0.1 .mu.m from the surface is composed of CuO as a main
component can efficiently be obtained. Therefore, the present
invention can be made more effective.
Furthermore, by setting the volume fraction of the burning residue
remaining after burning in the range of about 30% to 89%,
volumetric shrinkage can be significantly suppressed during burning
to cause securely form a conductor pattern (copper pattern after
burning) without disconnection.
By using an acrylic copolymer having carboxyl groups in the side
chains as an organic binder, it is possible to perform development
with water or an alkali aqueous solution while suppressing the
occurrence of gelation. Also, the organic binder is useful as a
photosensitive organic binder.
A method of forming a copper pattern of the present invention uses
the photosensitive copper paste comprising the copper powder having
the surface coating of a copper oxide, at least the surface layer
having a thickness of about 0.1 .mu.m from the surface being
composed of CuO as a main component. Therefore, gelation of the
photosensitive copper paste and gelation of the coating after
drying can be sufficiently suppressed to form a fine copper pattern
with high precision.
A circuit board of the present invention comprises a fine and thick
circuit (copper pattern) formed by forming a predetermined copper
pattern by using the photosensitive copper paste of the present
invention and then burning the copper pattern, thereby permitting
realization of high-density wiring and high-speed signal which
cannot be realized by a conventional circuit board.
A method of producing a ceramic multilayer substrate of the present
invention uses the photosensitive copper paste of the present
invention comprising the copper powder having the surface coating
of a copper oxide, at least the surface layer having a thickness of
about 0.1 .mu.m from the surface being composed of CuO as a main
component. Therefore, gelation of the photosensitive copper paste
and gelation of the coating after drying can be sufficiently
suppressed to form a fine copper pattern with high precision,
thereby obtaining a ceramic multilayer substrate having excellent
adaptability to higher density wiring and higher speed signals.
The ceramic multilayer substrate of the present invention comprises
a fine and thick copper pattern formed on an insulating substrate
by using the photosensitive copper paste of the present invention
and burning the coating, thereby permitting realization of
higher-density wiring and higher-speed signal which cannot be
realized by a conventional ceramic multilayer substrate.
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